The present invention relates generally to transformers such as those used in power conversion systems. More particularly, the present invention relates to multi-phase transformers winding placement with different number of air ducts.
Multi-phase transformers such as 9 phase transformers, are configured to convert a 3-phase AC input power to a multi-phase (e.g. 9 phase) AC output power. Such transformers are typically designed to provide a desired output AC power. The output AC power generated by the transformer may be rectified or filtered before being supplied to a load.
Typically, a 9 phase transformer includes 3 coils constructed on a laminated core. Each coil is formed of several windings. For example, in many 9 phase transformers, each coil is formed of five separate windings. Thus, the 9 phase transformer is typically formed using 15 windings connected in series.
During operation, leakage inductance is present in each winding of the coil. The leakage inductance in each coil often is typically unequal due to placement of the windings and air ducts. Such unbalanced leakage inductance causes an increase in the total harmonic distortion in the input power.
One technique often employed to reduce leakage inductance is winding the coil in different layers, each layer including several windings. For example, for a coil including five separate windings, one layer may be formed using first two windings and a portion of the third winding and a second layer may be formed with the other portion of the third winding and the remaining two windings. However, constructing the coil in multiple layers causes excessive heat generation that can eventually damage the transformer if the winding size is not properly selected.
To reduce the cost or reduce the winding temperature, Cooling ducts are typically employed to dissipate the heat generated by the transformer. However, there is a constraint on the number of cooling ducts that can be accommodated in the transformer as an increased number of cooling ducts will increase the size and the cost of the system as well. Therefore, there is a need to design a multi-phase transformer with an effective cooling system.